MAX1612 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Bridge-Battery Backup Controllers for Notebooks

Bridge-Battery Backup Controllers
for Notebooks
BRIDGE
BATTERY
ALWAYS-ON
OUTPUT
+5V/3.3V _1µF
470k
470k
160k
100µF
22µH
BBATT
LX
LRO
PGND
MAX1612
FULL _MAX1613
ISET
CCMD
LBO
FB
DCMD
MAIN
BATTERY
MBR0530
22µF
2.2k
0.33µF
BBON
CC
4.7nF
LBI
CD
GND
68nF
SYSTEM
DC-DC
(MAX1630)
442k
20k
200k
Figure 3. Stand-Alone Application
The counter block can be used to estimate the charge
remaining in the battery. For example, if the maximum
expected charge time is 14 hours (C_CC = 60nF) and
the maximum expected discharge time is about 2 hours
(C_CD = 8.6nF), the battery reaches full charge in 14
hours with the FULL pin going high. If the bridge bat-
tery must supply the load for 1 hour, the counter will
decrement down to about half full. Recharging the bat-
tery will now require only 7 hours to reach all 1s in the
counter, signaling with FULL going high.
If both DCMD and CCMD are pulled low simultaneous-
ly, the counter defaults to the discharge mode. When
the bridge battery is supplying the circuit, it is consid-
ered to be in discharge mode (Table 1).
Charge Current Selection (ISET)
A resistor between ISET and a voltage higher than the
bridge battery sets the charging rate. The switch is
open when CCMD is high and is turned on when
CCMD is pulled low (assuming DCMD is high). If the
voltage at ISET falls below 0.4V, the internal counter
resets to all 0s. The internal high-voltage switch has a
typical on-state voltage drop of 1V (Figure 1).
Therefore, the charge current equals:
I_ISET = [ (V_CHARGE - V_BBATT ) - 1V] / R_ISET
Linear-Regulator Output (LRO)
The linear-regulator output, LRO, is set at +5.0V for the
MAX1612 and at +3.3V for the MAX1613, with a toler-
ance of ±6%. For powering external circuitry such as
the microcontroller shown in Figure 4, LRO is guaran-
teed to deliver up to 10mA while maintaining regulation.
If the voltage at the linear-regulator input falls below the
operating range, an undervoltage-lockout feature shuts
down the entire device.
Table 1. CCMD, DCMD Truth Table
DCMD
CCMD
COUNTER ISET SWITCH
0
0
Count Down
Off
0
1
Count Down
Off
1
0
Count Up
On
1
1
No Count
Off
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